1. Field of the Invention
The present invention relates to a passive device embedded in a substrate and a substrate with a passive device embedded therein, and more particularly, to a passive device embedded in a substrate and a substrate with a passive device embedded therein that can improve a structure of an external electrode.
2. Description of the Related Art
With the trend of miniaturization of electronic products, the size and thickness of components are reduced according to the trend of the electronic products, and the components have been developed to be highly integrated and multifunctional. A PCB method according to this trend is a device embedded electronic circuit board.
Currently, a method of manufacturing a device embedded electronic circuit board embeds a device in a circuit board, forms layers by a layer lamination method which is a substrate manufacturing method, and electrically connects the layers using an interlayer connection method. As a typical interlayer connection method, there is a method of forming a via to conduct layers. As a via forming method, there is a laser or drilling method but a punching method using laser is most commonly used according to the trend toward precision.
A current interlayer connection method processes a via by a laser interconnection method and conducts layers by a plating method after an embedding process of embedding a device in a cavity and fixing and embedding the device by a lamination process which is a substrate process. In order to obtain a high yield in this process, laser processing deviation and accuracy when fixing the device in the cavity are very important.
In general, a via-hole is formed by laser and electrically connected to an electrode of an embedded passive device, for example, MLCC. In a technique of forming a via-hole by laser, a via size may be changed according to the thickness of laminated materials or post-processing after laser processing, but the bottom size of the via generally has a diameter of at least about 35 μm. According to the development trend of the substrate, since patterns get thinner and highly integrated, it is expected that the bottom size of the via is developed to a level of at least about 30 μm. It is because there may be problems with electrical connection when the diameter of the via is reduced to less than 30 μm.
FIG. 4 shows that a conventional passive device 6 is embedded in a conventional passive device embedded substrate. A circuit is formed after fixing the conventional passive device 6 by sequentially laminating insulating layers 4, a via-hole is formed by laser, and only an upper side is processed or vias 5a are processed on the upper and lower sides to electrically connect circuit patterns 5b and the passive device 6 as in FIG. 4. This conventional method could be applied without any problems since the size of the passive device 6 is large and the area of an external electrode exposed on the passive device 6 on the plane is sufficiently larger than the bottom size of the via 5a. 
The conventional method shown in FIG. 4 is a technique that can be applied only to the passive device 6 having a sufficient pad size during laser processing. However, the size of the passive device 6, for example, MLCC is gradually reduced to a size having difficulty in processing an upper pad with laser.
Referring to FIG. 5, in case of the embedded passive device 6, for example, MLCC, as the size thereof gets smaller, a part of the bottom of the via 5a may deviate from the pad, for example, the external electrode due to an alignment deviation when connecting the vias 5a to the upper and lower pads of the external electrode of the passive device 6. At this time, an alignment deviation of the via 5a may occur and thus the device may fail to function due to impact applied to the device when punching the via-hole.